Got an email from Bulb the other day saying they needed to increase my DD again as I was "at risk of building up debit soon".
This was clearly ridiculous, I was almost £500 in credit, and my last two monthly bills were < £200.
I dropped their support an email pointing this out and instructing them to leave the DD alone. I also asked about just paying the actual bill each month.
I was slightly shocked to get a reply at just after midnight ...
They basically offered to refund all my credit, and change my DD to take the actual billed usage each month.
I accepted.